In one aspect, the present invention relates to structures, including alignment films and alignment substrates useful in liquid crystal displays. In another aspect, the invention relates to display devices and other optical devices that utilize liquid crystal alignment films or substrates therein.
A common liquid crystal display, or xe2x80x9cLCD,xe2x80x9d contains an array of two-dimensional picture elements, or pixels. Although each pixel may, and customarily does, contain numerous optical elements, each comprises a liquid crystal cell. A liquid crystal cell generally comprises a liquid crystal material maintained between a pair of transparent substrates, and those substrates most commonly are made of glass or a polymeric material such as polyimide. Interposed between the liquid crystal material and the substrates are electrodes electrically connected to an outside signal device that, when electrically active, alter the state of the liquid crystal material. Such liquid crystal cells find application not only in displays, but also in other optical devices, including optical communication devices and other optical processing equipment.
In a liquid crystal cell, the molecules of liquid crystal material are aligned, or oriented, in a preferred direction along each of the substrates within the cell. Normally, this alignment is accomplished through the use of an alignment structure layer. Alignment layers generally are glass substrates or polymeric films, typically polyimides, that are mechanically rubbed in a single direction to impart an orientating effect on the liquid crystals with which they contact. The optical activity of the liquid crystal cell is in part a function of the relative orientation of the liquid crystals at the surface of each of the substrates and the ordered change in direction of the crystals between the substrates.
Such conventional alignment layers suffer myriad drawbacks. For example, the high temperatures necessary to process of many useful polymeric substrates prevent the incorporation of temperature-sensitive additives such as color dyes into the alignment structures. Also, the conventional rubbing, washing and drying steps used in manufacture of the layer films and substrates can be slow, expensive and introduce gross defects and low yields.
Briefly, in one aspect, the present invention provides an alignment structure useful in a liquid crystal display device that comprises a substrate having disposed thereon an oriented film or layer of a lyotropic liquid crystalline material. Particularly useful lyotropic liquid crystalline materials include a class of compounds known as chromonics. The structures of the invention can be made by coating the liquid crystalline material onto a substrate to provide an oriented film of the lyotropic material. The alignment substrates can also include one or more dyes or other additives and can thus, in addition to alignment and orientation, be made to perform polarizing, retarding and/or color filtering functions. The alignment structures can also be made with one or more additional layers, such as, for example, cholesteric retarders, non-optical polymers, etc.
In another aspect the invention provides optical devices. The optical devices include at least one liquid crystal material disposed between two substrates, wherein at least one of the substrates have disposed thereon an oriented film of a lyotropic liquid crystalline material. In other aspects, the invention provides methods of making such alignment structures and optical devices.